Organic semiconductor device, field-effect transistor, and their manufacturing methods

ABSTRACT

An organic semiconductor device is provided which includes an organic semiconductor layer and an insulating layer. The insulating layer is made of a cured material formed from a composition containing a resin and a crosslinking agent. The resin contains an organic resin having a hydroxyl group. The crosslinking agent contains a compound having at least two crosslinking groups. At least one of the crosslinking groups is a methylol group or an NH group. The composition contains the crosslinking agent in the range of 15 to 45 percent by weight relative to 100 parts by weight in total of the resin and the crosslinking agent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to organic semiconductor devices,field-effect transistors (FETs), and their manufacturing methods. Inparticular, the invention relates to a field-effect transistor includinga gate insulating layer which can be easily formed from a solution andfrom which low-molecular-weight impurities or the like do notprecipitate, and a method for manufacturing the same. The field-effecttransistor can exhibit a high mobility even if the substrate is made ofa resin.

2. Description of the Related Art

IC technology using organic semiconductor devices has recently receivedattention because they can be prepared at low cost and allow the use ofa flexible resin substrate. Because of these advantages, the organicsemiconductor devices promise to be applied to, for example, circuitsusing plastic boards, display drive circuits for electronic tags anddisplays, and memory.

An organic semiconductor device generally includes a substrate,insulating layers, electrodes, and an organic semiconductor layer. Amongsuch organic semiconductor devices is a thin-film field-effecttransistor including a gate insulating layer, a gate electrode, a sourceelectrode, a drain electrode, and an organic semiconductor layer.

In a field-effect transistor using an organic semiconductor as thesemiconductor layer, when the voltage (gate voltage, Vg) applied to thegate electrode is varied, the electric charge (carrier) at the interfacebetween the gate insulating layer and the organic semiconductor layerincreases or decreases. As a result, the value of drain-source current(Id, negative when flows from the drain electrode to the sourceelectrode) flowing from the source electrode to the drain electrodethrough the organic semiconductor is varied. Thus, the field-effecttransistor functions. The field-effect transistor functioning as themost ideal switching device can switch the states where carrier path ispresent and absent.

In fact, high-performance organic semiconductor devices are produced byapplying a solution of an organic semiconductor compound, such aspolyalkylthiophene or poly(thienylenevinylene) (see Assadi A. et al.,“Field-effect mobility of poly(3-hexylthiophene)”, Appl. Phys. Lett.,vol. 53, p. 195 (1988); Fuchigami H. et al., “Polythienylenevinylenethin-film transistor with high carrier mobility”, Appl. Phys. Lett.,vol. 63, p. 1372 (1993); and Japanese Patent Laid-Open No. 10-190001).

In order to produce an inexpensive and flexible device, the electrodesand the insulating layers can be formed on a flexible resin substrate bycoating or printing. However, the smoothness and flatness of the resinsubstrate is extremely inferior to those of silicon or glass substrates.Also, wet processes, such as printing, are easily affected by thesurface state of the substrate. It is therefore difficult to form aninsulating gate insulating layer with a uniform thickness and sufficientinsulation properties on the resin substrate. Accordingly, the leakcurrent from the source electrode to the drain electrode increasesdisadvantageously.

For the production of the organic semiconductor device on a flexibleresin substrate, the components overlying the substrate, such as thegate insulating layer and the organic semiconductor layer, arepreferably formed at low temperatures of 200° C. or less. The resinsubstrate may be softened and degraded in an atmosphere of hightemperature.

Known insulating layers will be illustrate below.

For example, Simoda et al. have produced an field-effect transistorincluding an insulating layer formed of polyvinylphenol (PVP), andelectrodes and an organic semiconductor layer formed by ink jet printing(Simoda T. et al., “Organic transistor fabricated by ink-jet printing”Oyo-buturi, Vol. 70, p. 1452 (2001). Veres et al. have produced afield-effect transistor including a polytriallylamine organicsemiconductor layer on an insulating layer having a low relativedielectric constant (Veres B. J. et al., “Low-k insulator as the choiceof dielectrics in organic field-effect transistors”, vol. 13, p. 199(2003)). Both the studies above use thermoplastic resins for theinsulating layers. The thermoplastic resin insulating layers exhibithigh workability, but have problems with solvent resistance and thermalstability. Thus, the thermoplastic resin insulating layer is unsuitablefor use in a multilayer structure, and it is difficult to form a highlyinsulating thin, dense layer.

Other approaches have been reported in which the insulating layer isformed of a thermosetting resin prepared by adding a methylated oracylated melamine-formaldehyde resin to PVP (Japanese Patent Laid-OpenNo. 2004-128469; Zschieschang, et al., “Flexible Organic Circuits withPrinted Gate Electrodes”, Advanced Materials, vol. 15, p. 1147 (2003)).This type of insulating layers may allow unreacted polar groups toremain in the layer after baking the resin at low temperatures at 200°C. or less, and the insulation properties may be reduced due tohygroscopicity or the like.

In addition, US2004094761 A1 and WO2002/009190 have disclosed improvedinsulating layers.

Each insulating layer above cannot ensure a high insulation orreliability if it is baked at a low temperature at which the plasticsubstrate can be maintained. If a catalyst or the like is added so thatthe insulating layer can be cured at a low temperature, the catalyst mayundesirably contaminate the organic semiconductor layer. Thus, it hasbeen difficult to achieve a field-effect transistor including an organicsemiconductor layer with a high mobility and reliability.

As described above, it has been difficult to form a highly insulatinguniform organic layer on a resin substrate in inexpensive manufacturingprocesses of field-effect transistors using organic semiconductors.Although thermally curable resin compositions prepared by adding acrosslinking agent to a thermoplastic resin, which is easy to apply forfilm formation, are useful to solve the difficulty, the thermallycurable resin compositions cannot be sufficiently cured to form aninsulating layer in the absence of a catalyst. Thus, it is difficult toform a highly insulating layer not adversely affecting the organicsemiconductor layer. This is a challenge in the formation of not onlythe gate insulating layer, but also other insulating layers, and is alsoa challenge to field-effect transistors and other devices using organicsemiconductors.

SUMMARY OF THE INVENTION

The inventors of the present invention has found that an insulatinglayer made of a thermally cured material formed from a curable resincomposition containing a resin having a specific substituent and acrosslinking agent having a specific crosslinking group is suitable fororganic semiconductor devices. In particular, the use of the insulatinglayer as a gate insulating layer can achieve a field-effect transistorin which current leakage from the gate electrode to the source or drainelectrode is extremely reduced.

According to an aspect of the present invention, there is provided anorganic semiconductor device including at least an organic semiconductorlayer and an insulating layer. The insulating layer is made of a curedmaterial formed from a composition containing a resin and a crosslinkingagent. The resin contains an organic resin having a hydroxyl group. Thecrosslinking agent has at least two crosslinking groups. At least one ofthe crosslinking groups is a methylol group or an NH group. Thecomposition contains the crosslinking agent in the range of 15 to 45percent by weight relative to 100 parts by weight in total of the resinand the crosslinking agent. In other words, relative to 100 parts byweight in total of the resin and the crosslinking agent, 15 to 45 partsby weight of the crosslinking agent is added.

In another aspect, the invention is directed to a field-effecttransistor including at least an organic semiconductor layer and aninsulating layer. The insulating layer is made of a cured materialformed from a composition containing a resin and a crosslinking agent.The resin contains an organic resin having a hydroxyl group. Thecrosslinking agent has at least two crosslinking groups. At least one ofthe crosslinking groups is a methylol group or an NH group. Thecomposition contains the crosslinking agent in the range of 15 to 45percent by weight relative to 100 parts by weight in total of the resinand the crosslinking agent. In other words, 15 to 45 parts by weight ofthe crosslinking agent is added.

In the field-effect transistor, the insulating layer can be a gateinsulating layer.

In the organic semiconductor device and the field-effect transistor, thecrosslinking agent can contain at least one compound selected from amongthe compounds expressed by the following general formulas:

In the formulas, R₁ and R₃ each represent at least one selected from thegroup consisting of hydrogen, halogen, hydroxyl, thiol, amino, nitro,cyano, carboxyl, amido, and aryl, and alkyl, alkenyl, alkynyl, alkoxyl,alkylthio, hydroxyalkyl and acyl having carbon numbers in the range of 1to 12. R₂ and R₄ each represent at least one selected from the groupconsisting of alkoxymethyl and acyloxymethyl having carbon numbers inthe range of 1 to 6. R₅ represents a u-valent organic group and urepresents an integer in the range of 1 to 5. n represents an integer inthe range of 1 to 6, m represents an integer in the range of 0 to 5, and2≦n+m≦6 holes. s Represents an integer in the range of 1 to 5, trepresents an integer in the range of 0 to 4, and 2≦s+t≦5 holes. TheR₃'s of the groups bound to the R₅ may be the same or different, and theR₄'s may also be the same or different.

R₆, R₇, R₈, R₉, R₁₀, and R₁₁ each represent at least one selected fromthe group consisting of —CH₂OH, —H, and —CH₂OR₁₆, and alkyl, alkenyl,alkynyl, alkoxyl, alkylthio, hydroxyalkyl and acyl having carbon numbersin the range of 1 to 12. At least one of the R₆, R₇, R₈, R₉, R₁₀, andR₁₁ is —CH₂OH or —H and at least two of the R₆, R₇, R₈, R₉, R₁₀, and R₁₁are —CH₂OH, —H, or —CH₂OR₁₆. R₁₂, R₁₃, R₁₄, and R₁₅ each represent atleast one selected from the group consisting of —CH₂OH, —H, and—CH₂OR₁₈, and alkyl, alkenyl, alkynyl, alkoxyl, alkylthio, hydroxyalkyland acyl having carbon numbers in the range of 1 to 12. At least one ofthe R₁₂, R₁₃, R₁₄, and R₁₅ is —CH₂OH or —H and at least two of the R₁₂,R₁₃, R₁₄, and R₁₅ are —CH₂OH, —H, or —CH₂OR₁₈. R₁₆ and R₁₈ eachrepresent at least one selected from the group consisting ofalkoxymethyl and acyloxymethyl having carbon numbers in the range of 1to 6. The R₁₆'s may be the same or different and the R₁₈'s may be thesame or different.

In the organic semiconductor device and the field-effect transistor, thehydroxyl group of the resin can be a phenolic hydroxyl group.

The resin having the phenolic hydroxyl group can be a phenol resinand/or a polyvinylphenol resin.

The insulating layer can have a volume resistivity of about 1×10¹³ Ω·cmor more.

The organic semiconductor layer of the field-effect transistor cancontain a porphyrin compound.

The organic semiconductor device and field-effect transistor can furtherinclude a substrate that is at least partially made of a resin.

In still another aspect, the invention is directed to a method formanufacturing an organic semiconductor device including at least anorganic semiconductor layer and an insulating layer. The method includesthe step of forming the insulating layer by applying a curable resincomposition containing a resin and a crosslinking agent, and thenheating the curable resin composition. The resin contains an organicresin having a hydroxyl group, and the crosslinking agent has at leasttwo crosslinking groups. At least one of the crosslinking groups is amethylol group or an NH group. Relative to 100 parts by weight in totalof the resin and the crosslinking agent, 15 to 45 parts by weight of thecrosslinking agent is added.

The invention is also directed to a method for manufacturing afield-effect transistor including at least an organic semiconductorlayer and an insulating layer. The method includes the step of formingthe insulating layer by applying a curable resin composition containinga resin and a crosslinking agent, and then heating the curable resincomposition. The resin contains an organic resin having a hydroxylgroup, and the crosslinking agent has at least two crosslinking groups.At least one of the crosslinking groups is a methylol group or an NHgroup. Relative to 100 parts by weight in total of the resin and thecrosslinking agent, 15 to 45 parts by weight of the crosslinking agentis added.

The crosslinking agent used in the method for manufacturing the organicsemiconductor device or the field-effect transistor can contain at leastone compound selected from among the compounds expressed by the generalformulas shown above.

The curable resin composition can be heated at a temperature in therange of 120 to 220° C.

The crosslinking agent used herein refers to a compound havingcrosslinking groups, each reacting with the hydroxyl group of the resin,optionally in the presence of a catalyst, to form a bond. Thecrosslinking groups include a group that can react with the hydroxylgroup of the resin after removing a protecting group (for example, analkyl group provided for reducing the reactivity of the crosslinkinggroup). The crosslinking agent has at least two crosslinking groups, andthe crosslinking groups are either crosslinking group having noprotecting group (for example, methylol and NH groups), or crosslinkinggroup from which a protecting group can be removed by a proton releasedfrom the methylol group or the NH group of the crosslinking agent in theabsence of a catalyst.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic fragmentary enlarged sectional view of afield-effect transistor including a gate electrode, a gate insulatinglayer, a source electrode, a drain electrode, and an organicsemiconductor layer, according to an embodiment of the presentinvention.

FIG. 2 is a schematic sectional view of the structure of field-effecttransistors of Examples 1 to 19 and Comparative Examples 2 to 5, thefield-effect transistors each including a substrate, a gate electrode, agate insulating layer, a surface treatment layer, an organicsemiconductor layer, a source electrode, and a drain electrode.

FIG. 3 is a plot of electrical characteristics of the field-effecttransistor used in Example 5 of the present invention.

FIG. 4 is a plot of electrical characteristics of the field-effecttransistor used in Example 53 to 55 and comparative example 14 and 15 ofthe present invention.

DESCRIPTION OF THE EMBODIMENTS

An organic semiconductor device according to an embodiment of thepresent invention includes an organic semiconductor, insulators, andelectric conductors.

The insulators cover the electric conductors serving as electrodes toestablish electrical insulation between the electric conductors andbetween the electric conductors and the organic semiconductor. Exemplaryinsulators include insulating interlayers, device separation films, andgate insulating films. The insulators also include members providedbetween the organic semiconductor or the electric conductors and theoutside of the device, such as a sealant or a protecting member.

The insulators are generally in a form of a layer or a film, and may bereferred to as insulating layers or insulating films in the description.However, the insulating layers or the insulating films used herein arenot complete layers or films, and may have, for example, island-shapedstructures.

A field-effect transistor including an organic semiconductor accordingto an embodiment of the present invention will now be described.

The field-effect transistor includes an organic semiconductor layer,insulators, and electric conductors. The electric conductors of thefield-effect transistor include a gate electrode, a source electrode,and a drain electrode. The organic semiconductor layer responds to thevoltage applied to the gate electrode. Specifically, the electricalcharacteristics of the organic semiconductor layer are changed dependingon the electric field produced by applying a voltage to the gateelectrode. More specifically, the electrical conductivity of the organicsemiconductor layer, or the current flowing through the organicsemiconductor layer, is varied depending on the changes in electricfield. At least one of the insulators of the field-effect transistor isdisposed between the gate electrode and the organic semiconductor layerto serve as a gate insulating layer.

The gate insulating layer not only electrically insulates the gateelectrode from the organic semiconductor layer, but also induces apositive or negative charge at the interface with the organicsemiconductor when a voltage is applied to the gate electrode.

The gate insulating layer can also be used to insulate the gateelectrode from the source electrode and the drain electrode.

In addition to the gate insulating layer, the field-effect transistorincludes other insulating layers, such as a sealant for insulating theelectrodes and the organic semiconductor layer from the outside, and aninsulating interlayer or a device separation film for insulating oneelectrode from another or one transistor from another.

FIG. 1 is a schematic sectional view of an organic semiconductor device(field-effect transistor) according to an embodiment. The organicsemiconductor device includes a substrate 1, a gate electrode 2, a gateinsulating layer 3, a source electrode 4, a drain electrode 5, and anorganic semiconductor layer 6. The gate electrode 2 is formed on thesurface of the substrate 1 and covered with the gate insulating layer 3.The source electrode 4 and the drain electrode 5 are formed with adistance on the surface of the gate insulating layer 3. The sourceelectrode 4, the drain electrode 5, and the surface between theseelectrodes of the gate insulating layer 3 are covered with the organicsemiconductor layer 6. The source and drain electrodes 4 and 5 are incontact with the organic semiconductor layer 6. Although the embodimentillustrates a typical field-effect transistor, the device may be avertical transistor or any other type of transistor.

As mentioned above, the gate insulating layer used in the embodiment notonly electrically insulates the gate electrode from the organicsemiconductor layer, but also induces a positive or negative charge atthe interface with organic semiconductor when a voltage is applied tothe gate electrode. In order to induce the charge efficiently, it ispreferable that the insulating layer and the organic semiconductor layerform a uniform interface. The inventors of the present invention haveconducted intense research for a material which can form a thininsulating layer having a uniform surface even on an uneven electrodeformed on a resin substrate, and from which a catalyst or an uncuredcomponent does not precipitate at the interface between the insulatinglayer and the organic semiconductor layer nor thus contaminate thelayers. As a result, it has been found that a cured material formed froma composition containing a specific organic resin and crosslinking agentcan be a proper insulating layer.

The cure material suitable for the insulating layer can be formed of acomposition containing an organic resin having a hydroxyl group and acrosslinking agent having at least two crosslinking groups at least oneof which is a methylol group or a NH group.

The resin having a hydroxyl group can be a resin having an aliphaticalcoholic hydroxyl group or a phenolic hydroxyl group. Examples of theresin having an aliphatic alcoholic hydroxyl group include, but notlimited to, poly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate), poly(hydroxypropyl methacrylate), poly(hydroxypropylacrylate), poly(4-vinylcyclohexanol), polyvinyl alcohol, and theircopolymers. Examples of the resin having a phenolic hydroxyl groupinclude, but not limited to, phenol resins, such as phenol novolakresins, cresol novolak resins and their modified resins, andpolyvinylphenols and their copolymers.

Among these, preferred are resins having a phenolic hydroxyl group. Theresins having a phenolic hydroxyl group can be easily dissolved invarious types of solvent, and accordingly easily applied onto varioustypes of substrate to form a uniform thickness. Besides, such resins canbe a strong and highly insulating film after being cured.

The resin having a hydroxyl group used in the embodiment can be apolymer or an oligomer having a number average molecular weight (Mn)between 250 and less than 500,000. A resin having an Mn of less than 250may result in a film having an insufficient strength after being cured.A resin having an Mn of 500,000 or more may rapidly increase theviscosity in a solution to degrade the film formability. Preferred Mn isbetween 350 and less than 200,000.

As the molecular weight distribution of the resin is reduced, the meltviscosity during heating and melting becomes uniform, and accordinglythe uniformity in thickness and the insulation properties of theresulting film can be increased. The preferred molecular weightdistribution is therefore 2.5 or less. More preferably, the molecularweight distribution is 2 or less.

In the insulating layer of the organic semiconductor device, the contentof low-molecular-weight components, which are likely to contaminate theorganic semiconductor layer, is preferably low. Therefore the insulatinglayer is preferably formed of a resin containing no low-molecular-weightcomponents, such as monomers. It is however difficult to eliminatelow-molecular-weight components completely from the resin. In theembodiment of the present invention, the resin can contains 5 percent byweight or less, preferably 2 percent by weight or less, of monomersrelative to the total weight of the resin before adding the crosslinkingagent.

In the insulating layer, the content of alkali metals that are likely tocontaminate the organic semiconductor layer, such as sodium, isextremely low. Specifically, the sodium content can be 20 ppm or less,and preferably 5 ppm or less. The sodium and other alkali metals in theinsulating layer can be removed by repeatedly washing the insulatinglayer with water, or by allowing the thermally curable resin compositionfor forming the insulating layer through an ultrafilter or anion-exchange resin. However, if the resin contains too much alkalimetal, they are difficult to remove by the above process. Therefore thesodium content in the resin is preferably 20 ppm or less.

The softening point of the resin can be in the range of 60 to 170° C. Aresin having a softening point of less than 60° C. may have aninsufficient strength after being cured. A resin having a softeningpoint of more than 170° C. may not sufficiently reflow over the resinsubstrate when it is cured by heating, and thus may make it difficult toform an even film on the surface of the electrode. Preferably, thesoftening point is in the range of 70 to 150° C.

The resin content in the cured material can be in the range of about 30to 90 percent by weight relative to the total weight of the curedmaterial. A resin content of less than 30 percent by weight may not leadto a sufficiently strong uniform film. A resin content of more than 90percent by weight may not lead to a sufficiently cured film, andaccordingly the resulting film may not be resistant to heat or solvents.Preferably, the resin content in the cured material is in the range ofabout 45 to 85 percent by weight.

The strength of the cured film can be increased by combined use of aphenol resin and a crosslinking agent.

The crosslinking agent has at least two crosslinking groups, and atleast one of the crosslinking groups is a methylol group or an NH group.

The methylol group reacts with the resin to form a covalent bond byheating. Such a methylol group may be a hydroxymethyl group bound to abenzene ring directly or to an amino group of a melamine ring. Also, themethylol group easily releases a proton. The proton removes a protectinggroup of other crosslinking groups so that the crosslinking groups reactwith the hydroxyl group of the resin.

The NH group releases a proton that removes the protecting group of thecrosslinking groups, as with the methylol group. In addition, the NHgroup reacts with the resin or other crosslinking groups to form acovalent bond.

Such an NH group may be derived from an amino group on a melamineskeleton. One of the hydrogen atoms of the amino group is replaced witha crosslinking group. Since the amino group (—NH₂) on the melamineskeleton can be expressed by H—NH—, the NH of the amino group can be theNH group as the crosslinking group of the embodiment. The NH group ispreferably expressed by —N═CR₂₀—NH— (wherein R₂₀ represents an organicgroup but not proton, and —N═CR₂₀ may form a ring system). This formeasily releases H.

Examples of the crosslinking agent having at least two crosslinkinggroups at least one of which is a methylol group or an NH group includethe compounds expressed by the following general formulas:

In the formulas, R₁ and R₃ each represent at least one selected from thegroup consisting of hydrogen, halogen, hydroxyl, thiol, amino, nitro,cyano, carboxyl, amido, and aryl, and alkyl, alkenyl, alkynyl, alkoxyl,alkylthio, hydroxyalkyl and acyl having carbon numbers in the range of 1to 12. R₂ and R₄ each represent at least one selected from the groupconsisting of alkoxymethyl and acyloxymethyl having carbon numbers inthe range of 1 to 6. R₅ represents a u-valent organic group and urepresents an integer in the range of 1 to 5. n represents an integer inthe range of 1 to 6, m represents an integer in the range of 0 to 5, and2≦n+m≦6 holes. s Represents an integer in the range of 1 to 5, trepresents an integer in the range of 0 to 4, and 2≦s+t≦5 holes. TheR₃'s of the groups bound to the R₅ may be the same or different, and theR₄'s may also be the same or different.

R₆, R₇, R₈, R₉, R₁₀, and R₁₁ each represent at least one selected fromthe group consisting of —CH₂OH, —H, and —CH₂OR₁₆, and alkyl, alkenyl,alkynyl, alkoxyl, alkylthio, hydroxyalkyl and acyl having carbon numbersin the range of 1 to 12. At least one of the R₆, R₇, R₈, R₉, R₁₀, andR₁₁ is —CH₂OH or —H and at least two of the R₆, R₇, R₈, R₉, R₁₀, and R₁₁are —CH₂OH, —H, or —CH₂OR₁₆. R₁₂, R₁₃, R₁₄, and R₁₅ each represent atleast one selected from the group consisting of —CH₂OH, —H, and—CH₂OR₁₈, and alkyl, alkenyl, alkynyl, alkoxyl, alkylthio, hydroxyalkyland acyl having carbon numbers in the range of 1 to 12. At least one ofthe R₁₂, R₁₃, R₁₄, and R₁₅ is —CH₂OH or —H and at least two of the R₁₂,R₁₃, R₁₄, and R₁₅ are —CH₂OH, —H, or —CH₂OR₁₈. R₁₆ and R₁₈ eachrepresent at least one selected from the group consisting ofalkoxymethyl and acyloxymethyl having carbon numbers in the range of 1to 6. The R₁₆'s may be the same or different and the R₁₈'s may be thesame or different.

Examples of the crosslinking agent having at least one methylol groupare listed below, but not limited to:

Examples of the crosslinking agent having at least one NH group arelisted below, but not limited to:

The methylol group is generally formed by condensation of formalin witha phenol compound in the presence of an alkali, or by reduction of anester with lithium aluminium hydride. The methylol compound thussynthesized may contain a residual alkali metal, such as sodium. Theresidual alkali metal may contaminate the organic semiconductor layerafter curing of the insulating layer. It is therefore preferable thatthe alkali metal remaining in the crosslinking agent be removed as muchas possible. Specifically, the sodium content in the crosslinking agentcan be about 20 ppm or less, preferably 5 ppm or less, relative to thetotal amount of the crosslinking agent.

Relative to 100 parts by weight in total of the resin and thecrosslinking agent, 15 to 45 parts by weight of the crosslinking agentcan be added. Less than 15 parts or more than 45 parts by weight of thecrosslinking agent disadvantageously requires too long curing time,which may cause the surface of the resulting film to have a higherroughness, and also degrade the uniformity of a surface treatment layerand an organic semiconductor layer on the resulting film. Preferably, 20to 40 parts by weight of the crosslinking agent is added to 100 parts byweight in total of the resin and the crosslinking agent.

For forming the insulating layer, the reaction between the resin and thecrosslinking agent (curing reaction by crosslinking) may need to becontrolled depending on the state of the surface underlying theinsulating layer. In such a case, a small amount of catalyst can beadded.

Catalysts suitable for the reaction between the resin and thecrosslinking agent include: carboxylic acids, such as formic acid,acetic acid, and oxalic acid; and sulfonic acids, such asp-toluenesulfonic acid and camphorsulfonic acid. Among these, preferredare sulfonic acids, such as p-toluenesulfonic acid, camphorsulfonicacid, and trifluoromethanesulfonic acid. In order to enhance thestability of the solution, an amine sulfonate can be used. Such aminesulfonates include pyridine p-toluenesulfonate.

A photoacid catalyst may be used. Examples of the photoacid catalystinclude trifluoromethanesulfonic acid, hexafluorophosphoric acid,diallyliodonium salts such as 9,10-dimethoxyanthracenesulfonic acid,triallylsulfonium salts, o-nitrobenzyl esters, andbis(trichloromethyl)-s-triazine compounds. If a photocatalyst is used,light exposure and heating are required after film formation.

Relative to 100 g in total of the resin and the crosslinking agent,about below 3 mmol of catalyst can be added. More than 3 mmol ofcatalyst may not only degrade the stability of the solution, but alsocause an excessive amount of the catalyst to precipitate on the surfaceof the insulating layer, thus degrading the mobility. Preferably, aboutbelow 2 mmol of catalyst is added to 100 g in total of the resin and thecrosslinking agent.

Solvents for dissolving the resin and other components include ethyleneglycol monomethyl ether, methyl cellosolve acetate, diethylene glycolmonomethyl ether, propylene glycol, propylene glycol monomethyl ether,propylene glycol monobutyl ether, propylene glycol monomethyl etheracetate, toluene, xylene, methylethyl ketone, methylisobutyl ketone,cyclohexanone, ethyl 2-hydroxypropionate, butyl acetate, ethyl lactate,butyl lactate, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,and isobutanol. These organic solvents may be used singly or incombination.

Among these solvents, preferred are propylene glycol monomethyl ether,propylene glycol monomethyl ether acetate, ethyl lactate, butyl lactate,cyclohexanone, ethanol, and 1-butanol, from the viewpoint of ease ofleveling.

The concentration of the resin in solution is adjusted according to thethickness of the film, and is preferably about 1 to 50 percent byweight. The resin solution is applied by spin casting, casting, dipping,die coating, slit coating, dropping, offsetting, offset or screenprinting, or ink-jetting. In order to maintain the smoothness of theresulting film, it is preferable that the resin solution contain dust orforeign matter as little as possible. Accordingly, the resin solution ispreferably filtered through a membrane filter.

In order to enhance the wettability on and the contact with thesubstrate or electrode, of the resin solution, a surfactant or acoupling agent may be added to the resin solution to the extent that theinsulation and other electrical properties do not deteriorate.

The thermally curable resin composition can be cured by heating at about100 to 200° C. The curable resin composition melted by heating can beallowed to flow to planarize the asperities of the surface of thesubstrate before curing. If the curing temperature is lower than 100°C., the resin cannot be sufficiently cured and consequently theresulting film cannot have a high deflection temperature and a highstrength. If the curing temperature is higher than 200° C., thethermally curable resin composition may be cured before it issufficiently spread, by rapid increase of temperature, and consequentlythe surface of the substrate may not be planarized. The resin can beheated by a variety of techniques, such as in a hot air circulationoven, a vacuum oven and an electric furnace, on a hot plate, and with aninfrared lamp.

Whether the insulating layer has been sufficiently cured can be examinedby measuring the solvent resistance, the infrared spectrum, or therefractive index. In particular, the measurement of the solventresistance to dimethylformamide (DMF) is the simplest. When theinsulating layer does not dissolve or swell even by immersion in DMF for5 minutes, it is determined that the insulating layer has beensufficiently cured.

If the insulating layer is used as the gate insulating layer 3, thethickness of the gate insulating layer can be in the range of 100 nm to1 μm, depending on the surface state of the gate electrode. A thicknessof less than 100 nm makes it difficult to be a dense film on anelectrode with a rough surface. On the other hand, a thickness of morethan 1 μm increases the absolute value of the drain-source current Id,and accordingly a high gate voltage is required. The thickness of thegate insulating layer is preferably in the range of 150 nm to 800 nm.

The surface at the organic semiconductor layer side of the gateinsulating layer can have an average surface roughness (Ra′) of 5 nm orless. If the gate insulating layer has an Ra′ of more than 5 nm, thethickness and the crystal growth of the organic semiconductor layerformed on the gate insulating layer become nonuniform, and consequentlythe mobility may be reduced. Preferably, the Ra′ is in the range of 0.1to 3 nm. The average surface roughness (Ra′) mentioned herein ismeasured with a scanning probe microscope SPI 3800 (product name)manufactured by Seiko Instruments, and is a parameter of the smoothnessof a film surface.

The insulating layer used in the embodiment has high insulationproperties, and exhibits a volume resistivity of 1×10¹³ Ω·cm or moreunder an applied voltage of 40 V or less. The volume resistivitymentioned herein is obtained from leak current density measured with aparameter analyzer 4156C manufactured by Agilen.

The substrate 1 used in the embodiment can be prepared by formingsilicon, glass, a metal, or a resin into a plate, foil, film, or sheet.A resin substrate is particularly suitable from the viewpoint offlexibility and workability. Exemplary materials of the resin substrateinclude polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polyimide (PI), polyetherimide (PEI), polyethersulfone (PES),polysulfone (PSF), polyphenylene sulfide (PPS), polyether ether ketone(PEEK), polyacrylate (PAR), and polyamidoimide (PAI). The resinsubstrate may also be made of a polycycloolefin resin, an acrylic resin,polystyrene, ABS, polyethylene, polypropylene, a polyamide resin, apolycarbonate resin, a polyphenylene ether resin, or a cellulose resin.Alternatively, the substrate may be made of an organic-inorganiccomposite prepared by adding inorganic oxide particles or binding aninorganic material to these resins.

The surface of the substrate may be polished or coated with a resin oran inorganic oxide so as to be flat and smooth and have a solventresistance and a heat resistance. In the examples described below, thesubstrate whose surface is not coated may be referred to as an uncoatedsubstrate, for the distinction from the substrate whose surface iscoated with a resin. The coated substrate may be referred to as simply asubstrate.

For the formation of the electrodes, any electroconductive material canbe used without particular limitation. Exemplary electroconductivematerials include platinum, gold, silver, nickel, chromium, copper,iron, tin, antimony, lead, tantalum, indium, aluminum, zinc, magnesiumand their alloys, and electroconductive metal oxides such as indium tinoxide. The materials also include inorganic or organic semiconductorswhose electrical conductivity is enhanced by doping, such as siliconsingle crystal, polysilicon, amorphous silicon, germanium, graphite,polyacetylene, poly-p-phenylene, polythiophene, polypyrrole,polyaniline, poly(thienylenevinylene), and poly-p-phenylenevinylene. Forthe source electrode 4 or the drain electrode 5, a material having a lowelectric resistance at the surface in contact with the semiconductorlayer is preferably selected from the above-listed electrode materials.The electrode may be formed by, for example, sputtering, vapordeposition, printing using solution, dispersion liquid, or paste, orink-jetting. In particular, an aggregate of electroconductive particleshaving diameters between 5 nm or more and less than 2 μm, formed byprinting of solution, dispersion liquid, or paste or by ink-jetting ispreferably used as the electrode, because it can be easily formedwithout using vacuum equipment. Specifically, such an electrode isformed of, for example, a dispersion liquid or solution of anelectroconductive polymer, metal particles, a metal oxide, a slurry orpaste of carbon black, or an organic metal solution. Preferredelectroconductive polymers includepoly(ethylenedioxythiophene)/poly(4-styrene sulfonic acid) andpoly(p-aniline)/camphorsulfonic acid. Exemplary metal particles includesilver or gold particles of several tens of nanometers in diameter andnanoparticles of nickel or other metals. Exemplary metal oxides includeparticles of zinc oxide, titanium oxide, tin oxide, antimony oxide,indium oxide, bismuth oxide, indium oxide doped with tin, tin oxidedoped with antimony, and zirconium oxide. Exemplary organic metalsinclude silver salts of organic acids. The dispersion liquid or solutionof these particles may contain a small amount of surfactant or resin sothat the particles are uniformly dispersed. The surfaces of theparticles may be modified with organic molecules.

In the aggregate of electroconductive particles, electroconductiveparticles with diameters between, for example, 5 nm or more and lessthan 2 μm are in contact with each other to deposit. The particles maybe fused to bond to each other, or closely deposited.

In order to reduce the resistance, the material applied for theformation of the electrode is often subjected to some heat treatment. Inthis instance, the heating temperature can be in the range of 120 to200° C., in view of use of the resin substrate. The thickness of theelectrode can be, but depending on the specific resistance of theelectroconductive material, in the range of about 30 nm to 2 μm, in viewof ease of covering step heights during film deposition and theresistance of the film.

The organic semiconductor layer 6 of the embodiment can be made of aπ-electron conjugated aromatic compound, a chain compound, an organicpigment, or an organic silicone compound. Exemplary materials of theorganic semiconductor layer 6 include polyacens such as pentacene,tetracene, and anthracene, thiophene oligomer derivatives, phenylenederivatives, tetraazaporphyrin compounds such as phthalocyaninecompounds, porphyrin compounds, and low-molecular materials such ascyanine dye. The materials further include polymers such aspolyacetylene derivatives, polythiophene derivatives, andpolyphenylenevinylene derivatives, oligomers, and dendrimers. However,the material of the organic semiconductor layer is not particularlylimited to the above-listed compounds.

Preferably, the organic semiconductor layer 6 is made of a porphyrincompound. One of the typical porphyrin compounds may be benzoporphyrin.Benzoporphyrin can increase the mobility of the resulting device byapplying a solution of its precursor in a bicyclo form soluble inorganic solvent, and subsequently applying heat or any other energy tothe solution to convert into porphyrin crystal. Combined use of thislayer with the insulating layer can achieve a field-effect transistorexhibiting a uniform and high mobility and a high on/off ratio.

The field-effect transistor of the embodiment can have a mobility ofabout 1×10³ cm²/V·s or more and an on/off ratio of about 100 or more.

In order to align the orientation of the molecules or promote thecrystal growth of the organic semiconductor layer 6, the surface of thegate insulating layer 3, the source electrode 4, or the drain electrode5 may be modified by, for example, dry treatment using ozone, plasma, orhexamethyldisilazane gas, or wet treatment using a solution oftetraalkoxysilane, trichlorosilane, or a surfactant in an organicsolvent. Alternatively, the surface of the gate insulating layer 3 orthe source and drain electrodes 4 and 5 may be coated with a thinpolymer film to align the orientation or promote the crystal growth ofthe organic semiconductor layer 6, provided that the coating does notact as an electric resistance between the source and drain electrodes 4and 5 and the organic semiconductor layer 6.

The field-effect transistor is not necessarily in a form of a thin film,and may be three-dimensional.

Although the embodiment mainly illustrates the gate insulating layer ofthe field-effect transistor, the effect of preventing migration can beproduced not only by using the insulating layer of the embodiment as aninsulating layer or a sealant provided in transistors, but also by usingit as an insulating layer or a sealant provided in other types oforganic semiconductor device. Hence, the present is not limited to thefield-effect transistor.

EXAMPLES

The present invention will further be described with reference toexamples, but the invention is not limited to the examples.

Glass Substrate 1 with ITO Electrode

A 0.7 mm thick glass substrate provided with an indium tin oxide(hereinafter referred to as ITO) layer of about 150 nm in thickness waswashed with acetone and isopropyl alcohol and dried. The surfaceroughness (Ra′) of the substrate was measured with a scanning probemicroscope (SPI 3800, manufactured by Seiko Instruments) and resulted in7 nm.

Glass Substrate 2 with Silver Electrode

A 1 mm thick glass substrate was washed with acetone and isopropylalcohol and dried. The surface of the substrate was coated with adispersion liquid of silver particles in alcohol (Fine Sphere SVE 102,produced by Nippon Paint) by dipping, followed by baking at 180° C. for30 minutes in a hot air circulation oven. Glass substrate 2 with a 150nm thick silver electrode was thus prepared. The surface roughness (Ra′)of this substrate was 10 nm.

Resin Substrate 3 with Silver Electrode

A 188 μm thick uncoated substrate of PET (HLA-188, produced by TeijinDuPont Films) was provided with a 3 μm thick planarizing layer formed ofa cured material containing phenol novolak resin, melamine crosslinkingagent (CYMEL 303, produced by Cytec Industries), and an acid catalyst(Catalyst 4040, produced by Cytec Industries) at a weight ratio of60:40:2. The surface of the resulting resin substrate was coated with adispersion liquid of silver particles in alcohol (Fine Sphere SVE 102,produced by Nippon Paint) by dipping, followed by baking at 180° C. for30 minutes in a hot air circulation oven. A resin substrate 3 with a 150nm thick silver electrode was thus prepared. The surface roughness (Ra′)of this resin substrate was 10 nm.

Resin Substrate 4 with Silver Electrode

The surface of a 200 μm thick organic-inorganic hybrid substrate (HTSubstrate, manufactured by Nippon Steel Chemical) was coated with adispersion liquid of silver particles in alcohol (Fine Sphere SVE 102,produced by Nippon Paint) by dipping, followed by baking at 180° C. for30 minutes in a hot air circulation oven. A resin substrate 4 with a 150nm thick silver electrode was thus prepared. The surface roughness (Ra′)of this resin substrate was 10 nm.

Preparation of Organic Resin Solution 1

In 87 g of 1:1 mixed solvent of 1-butanol and ethanol, 9.75 g of phenolnovolak resin (PN, number average molecular weight: 770, molecularweight distribution: 1.5, sodium content: 0.1 ppm or less) as the resinand 3.25 g of 2,6-dihydroxymethyl-4-methylphenol (DHMP, sodium content:3 ppm or less) expressed by formula (2) as the crosslinking agent werecompletely dissolved at room temperature. Then, the solution wasfiltered through a 0.2 μm PTFE membrane filter to obtain organic resinsolution 1.

Preparation of Organic Resin Solution 2

Using 9.1 g of phenol novolak resin (PN, number average molecularweight: 770, molecular weight distribution: 1.5, sodium content: 0.1 ppmor less) as the resin and 3.9 g of2,2-bis(3,5-dihydroxymethyl-4-hydroxy)propane (BDHP, sodium content: 3ppm or less) expressed by formula (3) as the crosslinking agent, organicresin solution 2 was prepared in the same manner as organic resinsolution 1.

Preparation of Organic Resin Solution 3

Organic resin solution 3 was prepared in the same manner as organicresin solution 2 except that 1,3,5-trihydroxymethylbenzene (THMB, sodiumcontent: 3 ppm or less) expressed by formula (4) was used as thecrosslinking agent.

Preparation of Organic Resin Solution 4

Organic resin solution 3 was prepared in the same manner as organicresin solution 2 except that a crosslinking agent containing a melaminecompound having an NH group and a methylol group (Nikalac MX-750LM,produced by Sanwa Chemical, sodium content: 0.2 ppm or less) expressedby formula (5) was uses as the crosslinking agent.

Preparation of Organic Resin Solution 5

Organic resin solution 5 was prepared in the same manner as organicresin solution 2 except that an o-cresol novolak resin (o-CN, numberaverage molecular weight: 840, molecular weight distribution: 1.2,sodium content: 0.1 ppm or less) was used as the resin.

Preparation of Organic Resin Solution 6

Organic resin solution 6 was prepared in the same manner as organicresin solution 4 except that an o-cresol novolak resin (o-CN, numberaverage molecular weight: 840, molecular weight distribution: 1.2,sodium content: 0.1 ppm or less) was used as the resin.

Preparation of Organic Resin Solution 7

In 91 g of 1:1 mixed solution of 1-butanol and ethanol, 6.3 g ofpoly(4-vinylphenol)(VP-8000, produced by Nippon Soda, number averagemolecular weight: 11,000, molecular weight distribution: 1.1, sodiumcontent: 1 ppm or less) as the resin) and 2.7 g of2,2-bis(3,5-dihydroxymethyl-4-hydroxy)propane (sodium content: 3 ppm orless) as the crosslinking agent were completely dissolved at roomtemperature. Then, the solution was filtered through a 0.2 μm PTFEmembrane filter to obtain organic resin solution 7.

Preparation of Organic Resin Solution 8

Organic resin solution 8 was prepared in the same manner as organicresin solution 7 except that a melamine crosslinking agent having a NHgroup and a methylol group (Nikalac MX-750LM, produced by SanwaChemical, sodium content: 0.2 ppm or less) was used as the crosslinkingagent.

Preparation of Organic Resin Solution 9

Organic resin solution 9 was prepared in the same manner as organicresin solution 2 except that a methylated methylolmelamine crosslinkingagent (Nikalac MW-100LM, produced by Sanwa Chemical, sodium content: 0.2ppm or less) expressed by formula (6) was used as the crosslinkingagent.

Preparation of Organic Resin Solution 10

Organic resin solution 10 was prepared in the same manner as organicresin solution 9 except that 0.2 g of p-toluenesulfonic acid monohydrate(PTS) was added as a catalyst.

Preparation of Organic Resin Solution 11

Organic resin solution 11 was prepared in the same manner as organicresin solution 9 except that poly(4-vinylphenol)(VP-8000, produced byNippon Soda, number average molecular weight: 11,000, molecular weightdistribution: 1.1, sodium content: 1 ppm or less) was used as the resin.

Preparation of Organic Resin Solution 12

Organic resin solution 12 was prepared in the same manner as organicresin solution 11 except that 0.2 g of p-toluenesulfonic acidmonohydrate (PTS) was added as a catalyst.

In the following Examples 1 to 19 and Comparative Examples 1 to 5, theinsulating layer formed on each substrate was evaluated for itscharacteristics. Further, TFT 1 (Examples 20 to 36, Comparative Examples6 to 9) containing an metal-free benzoporphyrin and TFT 2 (Examples 37to 52, Comparative Examples 10 to 13) containing benzoporphyrin wereprepared using some of the substrates with insulating layers of theExamples and Comparative Examples. The mobilities and on/off ratios ofthese TFTs were evaluated.

Examples 1 to 19, Comparative Examples 1 to 5

Insulating Layer Formation and Thickness Measurement

Substrates 1 to 4 with an electrode were each coated with any one oforganic resin solutions 1 to 7 by dipping, followed by heating at 180°C. for 1 hour in a hot air circulation oven to form a cured organicresin layer (insulating layer). The thicknesses of the thermally curedresin layers were measured with a reflectance spectrophotometricthickness meter FE-3000 (product name) manufactured by OtsukaElectronics.

Average Surface Roughness Measurement

The average surface roughness (Ra) of each thermally cured resin layer(insulating layer) was measured with a scanning probe microscope SPI3800 (product name) manufactured by Seiko Instruments.

Evaluation of Solvent Resistance

The thermally cured resin layer (insulating layer) was immersed inroom-temperature dimethylformamide (DMF) for 5 minutes, and then thethickness was measured. When the difference between the thicknessesbefore and after DMF immersion was less than 2%, it was determined thatthe thermally cured resin layer has been sufficiently cured.

Evaluation of Insulation Properties

A 200 μm square gold electrode was formed on the thermally cured resinlayer by vacuum vapor deposition. Then, the leak current density when avoltage of 0 to 40 V was applied in the thickness direction was measuredwith a parameter analyzer 4156C (product name) manufactured by Agilent,and the volume resistivity at a voltage of 40 V was calculated from thefollowing Equation 1. The measurement was performed on 20 points foreach thermally cured resin layer, and the number of points that did notproduce dielectric breakdowns (number of non-breakdown points) wascounted.Volume resistivity (ρv)=1/current density (A/cm²)×voltage (V)/thickness(cm) [Ω·cm]  Equation 1

The characteristics of the insulating layers of Examples 1 to 19 andComparative Examples 1 to 5 are shown in Table 1. The solventresistances of the insulating layers whose difference between thethicknesses before and after DMF immersion was less than 2% wererepresented as “good”. The solvent resistances of the other insulatinglayers are represented as “poor”.

TABLE 1 Organic Non- resin Crosslinking Thickness Ra Solvent ρvbreakdown solution Resin agent Catalyst Substrate (nm) (nm) resistance(Ω · cm) points Example 1 Solution 1 PN DHMP — 1 600 <0.6 Good 2.9 ×10¹³ 20/20 Example 2 Solution 1 PN DHMP — 3 600 <0.6 Good 3.7 × 10¹³20/20 Example 3 Solution 2 PN BDHP — 1 520 <0.6 Good 3.9 × 10¹³ 20/20Example 4 Solution 2 PN BDHP — 2 500 <0.6 Good 4.1 × 10¹³ 20/20 Example5 Solution 2 PN BDHP — 3 500 <0.6 Good 4.3 × 10¹³ 20/20 Example 6Solution 2 PN BDHP — 4 500 <0.6 Good 4.2 × 10¹³ 20/20 Example 7 Solution3 PN THMP — 3 520 <0.6 Good 3.9 × 10¹³ 20/20 Example 8 Solution 4 PNMX-750LM — 1 500 <0.6 Good 3.3 × 10¹³ 20/20 Example 9 Solution 4 PNMX-750LM — 2 500 <0.6 Good 3.6 × 10¹³ 20/20 Example 10 Solution 4 PNMX-750LM — 3 500 <0.6 Good 4.7 × 10¹³ 20/20 Example 11 Solution 4 PNMX-750LM — 4 500 <0.6 Good 4.9 × 10¹³ 20/20 Example 12 Solution 5 o-CNBDHP — 3 450 <0.6 Good 4.2 × 10¹³ 20/20 Example 13 Solution 6 o-CNMX-750LM — 3 450 <0.6 Good 4.5 × 10¹³ 20/20 Example 14 Solution 7 VP-BDHP — 1 480 <0.6 Good 8.9 × 10¹³ 20/20 8000 Example 15 Solution 7 VP-BDHP — 3 480 <0.6 Good 1.3 × 10¹⁴ 20/20 8000 Example 16 Solution 8 VP-MX-750LM — 1 500 <0.6 Good 2.5 × 10¹⁴ 20/20 8000 Example 17 Solution 8VP- MX-750LM — 2 500 <0.6 Good 1.0 × 10¹⁴ 20/20 8000 Example 18 Solution8 VP- MX-750LM — 3 500 <0.6 Good 1.1 × 10¹⁴ 20/20 8000 Example 19Solution 8 VP- MX-750LM — 4 500 <0.6 Good 1.3 × 10¹⁴ 20/20 8000Comparative Solution 9 PN MW-100LM — 3 490 0.8 Poor 4.8 × 10¹² 13/20Example 1 Comparative Solution PN MW-100LM PTS 1 500 <0.6 Good 1.0 ×10¹⁴ 20/20 Example 2 10 (1.5 phr) Comparative Solution PN MW-100LM PTS 3500 <0.6 Good 1.2 × 10¹⁴ 20/20 Example 3 10 (1.5 phr) ComparativeSolution VP- MW-100LM — 3 500 1.0 Poor 7.0 × 10¹² 18/20 Example 4 118000 Comparative Solution VP- MW-100LM PTS 3 510 <0.6 Good 2.2 × 10¹⁴20/20 Example 5 12 8000 (1.5 phr)

Examples 20 to 36, Comparative Examples 6 to 9

Evaluation of TFT (FET) Characteristics

TFT 1 (Metal-Free Benzoporphyrin TFT)

FIG. 2 is a schematic sectional view of a transistor including any oneof the substrates including the insulating layer prepared in Examples 1to 19 and Comparative Examples 2 to 5. The transistor includes asubstrate 7, a gate electrode 8, a gate insulating layer 9, a surfacetreatment layer 10, an organic semiconductor layer 11, a sourceelectrode 12, and a drain electrode 13.

A 10 nm thick surface treatment layer 10 of methylsilsesquioxane ladderpolymer (Glass Resin GR-650, produced by Showa Denko) was formed on thesurface of each board (corresponding to Examples 1 to 19 and ComparativeExamples 2 to 5) prepared by depositing the gate electrode 8 and thegate insulating layer 9 on the substrate 7 in the same manner as in theabove-described processes.

The resulting surface treatment layers were each coated with a solutionof 1% metal-free tetrabicycloporphyrin, expressed by formula (7), inchloroform by spin coating. The resulting metal-freetetrabicycloporphyrin thin coating was baked at 220° C. for 5 minutes ona hot plate, thus forming a 70 nm thick organic semiconductor layer 11of metal-free tetrabenzoporphyrin expressed by formula (8).

The source electrode 12 and the drain electrode 13 were formed on theorganic semiconductor layer 11 with a metal deposition mask by vacuumvapor deposition. The electrodes were formed of gold. The ultimatevacuum in the vacuum deposition was 3×10⁻⁵ Pa and the temperature of theboard was set at room temperature. The distance between the sourceelectrode and the drain electrode (channel length L) was 50 μm; thelengths of the source and drain electrodes (channel width W) were 30 mm;the thickness of the gold deposition film was 100 nm. The resultingboard, or a transistor, was measured for the Vd-Id and Vg-Id curves witha parameter analyzer 4156C (product name) manufactured by Agilent. FIG.3 shows the Vg-Id curves of the transistor of Example 5.

The mobility μ (cm²/Vs) was calculated from Equation 2:Id=μ(CiW/2L)(Vg−Vth)²  Equation 2

In the equation, Ci represents the capacitance per unit area (F/cm²) ofthe gate insulating layer; W and L represent the channel width (mm) andthe channel length (μm), respectively; Id, Vg, and Vth represent draincurrent (A), gate voltage (V), and threshold voltage (V), respectively.The on/off ratio was defined as (maximum |Id|)/(minimum |Id|) when Vgwas swept from −40 to 40 V with Vd fixed at −40 V. Table 2 shows thecharacteristics of metal-free tetrabenzoporphyrin TFTs of Examples 20 to36 and Comparative Examples 6 to 9.

Examples 37 to 52, Comparative Examples 10 to 13

Evaluation of TFT (FET) Characteristics

TFT 2 (Tetrabenzoporphyrin copper complex TFT)

Transistors was produced in the same manner as the metal-free porphyrinTFT, TFT 1, except that each board of Examples 2 to 19 and ComparativeExamples 2 to 5, including the substrate and the insulating layer, wascoated with a thin film of tetrabicycleporphyrin copper complexexpressed by formula (9) in the same manner as in Examples 20 to 36, andthat the tetrabicycleporphyrin copper complex coating was baked at 220°C. for 5 minutes on a hot plate to form an organic semiconductor layer11 of tetrabenzoporphyrin copper complex expressed by formula (10).

Table 2 shows the characteristics of tetrabenzoporphyrin copper complexTFTs of Examples 37 to 52 and Comparative Examples 10 to 13.

TABLE 2 Metal-free Benzoporphyrin copper Insulating layer onbenzoporphyrin complex substrate μ (cm²/vs) on/off ratio μ (cm²/vs)on/off ratio Layer of Example 1 Example 20 0.03 14,000 — — Layer ofExample 2 Example 21 0.09 30,000 Example 37 0.7 11,000 Layer of Example3 Example 22 0.04 22,000 Example 38 0.35 5,000 Layer of Example 5Example 23 0.2  40,000 Example 39 1.0 14,000 Layer of Example 7 Example24 0.05 17,000 Example 40 0.4 11,000 Layer of Example 8 Example 25 0.0518,000 Example 41 0.35 8,500 Layer of Example 9 Example 26 0.06 18,000Example 42 0.4 9,000 Layer of Example 10 Example 27 0.35 55,000 Example43 1.4 24,000 Layer of Example 11 Example 28 0.15 34,000 Example 44 1.218,500 Layer of Example 12 Example 29 0.08 23,000 Example 45 0.7 10,500Layer of Example 13 Example 30 0.2  35,000 Example 46 1.1 22,000 Layerof Example 14 Example 31 0.07 20,000 Example 47 0.5 12,000 Layer ofExample 15 Example 32 0.07 18,000 Example 48 0.7 17,500 Layer of Example16 Example 33 0.08 21,000 Example 49 0.5 10,000 Layer of Example 17Example 34 0.07 19,000 Example 50 0.5 9,000 Layer of Example 18 Example35 0.15 33,000 Example 51 1.0 23,000 Layer of Example 19 Example 36 0.2542,000 Example 52 1.2 22,5000 Layer of Comparative Comparative 8.4 ×10⁻⁷ 1 Comparative 2.2 × 10⁻⁶ 1 Example 2 Example 6 Example 10 Layer ofComparative Comparative 1.2 × 10⁻⁶ 1 Comparative 4.2 × 10⁻⁶ 1 Example 3Example 7 Example 11 Layer of Comparative Comparative 5.6 × 10⁻³ 35Comparative 8.7 × 10⁻² 15 Example 4 Example 8 Example 12 Layer ofComparative Comparative 3.1 × 10⁻⁵ 5 Comparative 1.0 × 10⁻⁵ 1 Example 5Example 9 Example 13

Preparation of organic resin solution 13 to 16 In 87 g of2-methoxy-1-acetoxypropane, 13 g in total of phenol novolak resin (PN,number average molecular weight: 770, molecular weight distribution:1.5, sodium content: 0.1 ppm or less) as the resin and crosslinkingagent containing a melamine compound having an NH group and a methylolgroup (Nikalac MX-750LM, produced by Sanwa Chemical, sodium content: 0.2ppm or less) were completely dissolved at room temperature. Then, thesolutions were filtered through a 0.2 μm PTFE membrane filter to obtainorganic resin solutions 13 to 16. Relative to 100 parts by weight intotal of PN and Nikalac MX-750LM in each of the solutions, 20, 30, 40,and 50 parts by weight of the Nikalac MX-750LM were added, respectively.

Preparation of Organic Resin Solution 17

In 85 g of 1:1 mixed solvent of 1-butanol and ethanol, 15 g ofcrosslinking agent containing a melamine compound having an NH group anda methylol group (Nikalac MX-750LM, produced by Sanwa Chemical, sodiumcontent: 0.2 ppm or less) was completely dissolved at room temperature.Then, the solutions were filtered through a 0.2 μm PTFE membrane filterto obtain organic resin solution 17.

Insulating Layer Formation

Resin substrates 3 with silver electrode were each coated with any oneof organic resin solutions 13 to 17 by dipping, followed by heating at180° C. for 1 hour in a hot air circulation oven to form a cured organicresin layer (insulating layer). The thicknesses of the thermally curedresin layers were approximately 400 nm.

Evaluation of Solvent Resistance

The thermally cured resin layers (insulating layers) formed from organicsolutions 9 to 17 were immersed in room-temperature dimethylformamide(DMF) for 5 minutes. The difference between the thicknesses of thethermally cured resin layer (insulating layer) formed from organic resinsolution 17 before and after DMF immersion was over 10%.

Surface Treatment Layer Formation

A 5 nm thick surface treatment layer 10 of 3:1 mixed resin ofmethylsilsesquioxane ladder polymer (Glass Resin GR-650, produced byShowa Denko) and methyltrimethoxysilane was formed on the surface ofeach thermally cured resin layer (insulating layer).

A water contact angle of the resulting surface treatment layer wasmeasured with an automatic dynamic contact angle meter DCA-WZ (made byKyowa Interface Science Co., LTD.).

TFT 3 (Tetrabenzoporphyrin Copper Complex TFT)

The resulting surface treatment layers were each coated with a solutionof 1% tetrabicycloporphyrin copper complex in chloroform by spincoating. The resulting tetrabicycloporphyrin copper complex thin coatingwas baked at 210° C. for 15 minutes on a hot plate, thus forming a 100nm thick organic semiconductor layer 11 of tetrabenzoporphyrin coppercomplex.

The source electrode 12 and the drain electrode 13 were formed on theorganic semiconductor layer 11 with a metal deposition mask by vacuumvapor deposition. The electrodes were formed of gold. The resultingboard, or a transistor, was measured in the same manner as in Example 20to 52. Table 3 and FIG. 4 show the characteristics oftetrabenzoporphyrin copper complex TFTs of Examples 53 to 55 andComparative Examples 14 to 15.

Relative to 100 parts by weight in total of the resin and thecrosslinking agent, 50 parts or more by weight of the crosslinking agentcaused degradations of the TFT characteristics. In contrast, 20 to 40parts by weight of the crosslinking agent provided TFTs with highmobility and high On/Off ratio.

TABLE 3 Water contact angle of the Benzoporphyrin Organic Parts incomposition surface copper resin Crosslinking treatment layer Solventcomplex solution Resin agent (degree) resistance μ (cm²/vs) on/off ratioExample 53 Solution 80 20 83.3 Good 0.43 1,000 13 Example 54 Solution 7030 83.6 Good 1.24 3,000 14 Example 55 Solution 60 40 83.7 Good 0.681,000 15 Comparative Solution 50 50 81.8 Good  0.019 11 Example 14 16Comparative Solution 0 100 86.0 Poor 5.1 × 10⁻⁴ 3 Example 15 17

In the embodiments above, a curable resin composition containing nocatalyst or a small amount of acid catalyst is used for the insulatinglayer. The curable rein composition can provide a uniform and smooththin insulating layer having a high solvent resistance and highinsulation properties on the gate electrode. Consequently, the resultingfield-effect transistor can reduce the decreases of the on/off ratio andthe mobility, which is due to the migration of low-molecular-weightcomponents from the insulating layer.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No.2005-088938 filed Mar. 25, 2005, which is hereby incorporated byreference herein in its entirety.

1. An organic semiconductor device comprising: an organic semiconductorlayer; and an insulating layer made of a cured material formed from acomposition containing a resin and a crosslinking agent, wherein theresin contains an organic resin having a hydroxyl group, and thecrosslinking agent contains a compound having at least two crosslinkinggroups at least one of which is a methylol group or a NH group, andwherein the composition contains the crosslinking agent in the range of15 to 45 parts by weight relative to 100 parts by weight in total of theresin and the crosslinking agent.
 2. The organic semiconductor deviceaccording to claim 1, wherein the crosslinking agent contains at leastone compound selected from among the compounds expressed by thefollowing general formulas:

wherein R₁ and R₃ each represent at least one selected from the groupconsisting of hydrogen, halogen, hydroxyl, thiol, amino, nitro, cyano,carboxyl, amido, and aryl, and alkyl, alkenyl, alkynyl, alkoxyl,alkylthio, hydroxyalkyl and acyl having carbon numbers in the range of 1to 12; R₂ and R₄ each represent at least one selected from the groupconsisting of alkoxymethyl and acyloxymethyl having carbon numbers inthe range of 1 to 6; R₅ represents an u-valent organic group and urepresents an integer in the range of 1 to 5; n represents an integer inthe range of 1 to 6, m represents an integer in the range of 0 to 5, and2≦n+m≦6 holes; s represents an integer in the range of 1 to 5, trepresents an integer in the range of 0 to 4, and 2≦s+t≦5 holes; theR₃'s may be the same or different and the R₄'s may be the same ordifferent; R₆, R₇, R₈, R₉, R₁₀, and R₁₁ each represent at least oneselected from the group consisting of —CH₂OH, —H, and —CH₂OR₁₆, andalkyl, alkenyl, alkynyl, alkoxyl, alkylthio, hydroxyalkyl and acylhaving carbon numbers in the range of 1 to 12, at least one of the R₆,R₇, R₈, R₉, R₁₀, and R₁₁ is —CH₂OH or —H, and at least two of the R₆,R₇, R₈, R₉, R₁₀, and R₁₁ are —CH₂OH, —H, or —CH₂OR ₁₆; R₁₂, R₁₃, R₁₄,and R₁₅ each represent at least one selected from the group consistingof —CH₂OH, —H, and —CH₂OR₁₈, and alkyl, alkenyl, alkynyl, alkoxyl,alkylthio, hydroxyalkyl and acyl having carbon numbers in the range of 1to 12, at least one of the R₁₂, R1₃, R₁₄, and R₁₅ is —CH₂OH or —H, andat least two of the R₁₂, R₁₃, R₁₄, and R₁₅ are —CH₂OH, —H, or —CH₂OR₁₈;and R₁₆ and R₁₈ each represent at least one selected from the groupconsisting of alkoxymethyl and acyloxymethyl having carbon numbers inthe range of 1 to 6, the R₁₆'s may be the same or different and theR₁₈'s may be the same or different.
 3. The organic semiconductor deviceaccording to claim 1, wherein the hydroxyl group of the organic resin isa phenolic hydroxyl group.
 4. The organic semiconductor device accordingto claim 3, wherein the organic resin having the phenolic hydroxyl groupis a polyvinylphenol resin and/or a phenol resin.
 5. The organicsemiconductor device according to claim 1, wherein the insulating layerhas a volume resistivity of about 1×10¹³ Ω·cm or more.
 6. The organicsemiconductor device according to claim 1, further comprising asubstrate containing a resin.
 7. field-effect transistor comprising: anorganic semiconductor layer; an insulating layer made of a curedmaterial formed from a composition containing a resin and a crosslinkingagent, wherein the resin contains an organic resin having a hydroxylgroup, and the crosslinking agent contain a compound having at least twocrosslinking groups at least one of which is a methylol group or a NHgroup, and wherein said composition contains said crosslinking agent inthe range of 15 to 45 parts by weight relative to 100 parts by weight intotal of the resin and the crosslinking agent.
 8. The field-effecttransistor according to claim 7, wherein the insulating layer is a gateinsulating layer.
 9. The field-effect transistor according to claim 7,wherein the crosslinking agent contains at least one compound selectedfrom among the compounds expressed by the following general formulas:

wherein R₁ and R₃ each represent at least one selected from the groupconsisting of hydrogen, halogen, hydroxyl, thiol, amino, nitro, cyano,carboxyl, amido, and aryl, and alkyl, alkenyl, alkynyl, alkoxyl,alkylthio, hydroxyalkyl and acyl having carbon numbers in the range of 1to 12; R₂ and R₄ each represent at least one selected from the groupconsisting of alkoxymethyl and acyloxymethyl having carbon numbers inthe range of 1 to 6; R₅ represents an u-valent organic group and urepresents an integer in the range of 1 to 5; n represents an integer inthe range of 1 to 6, m represents an integer in the range of 0 to 5, and2≦n+m≦6 holes; s represents an integer in the range of 1 to 5, trepresents an integer in the range of 0 to 4, and 2≦s+t≦5 holes; theR₃'s may be the same or different and the R₄'s may be the same ordifferent; R₆, R₇, R₈,R₉, R₁₀, and R₁₁ each represent at least oneselected from the group consisting of —CH₂OH, —H, and —CH₂OR₁₆, andalkyl, alkenyl, alkynyl, alkoxyl, alkylthio, hydroxyalkyl and acylhaving carbon numbers in the range of 1to 12, at least one of the R₆,R₇, R₈, R₉, R₁₀, and R₁₁ is —CH₂OH or —H, and at least two of the R₆,R₇, R₈, R₉, R₁₀, and R₁₁ are —CH₂OH, —H, or —CH₂OR₁₆; R₁₂, R ₁₃, R ₁₄,and R₁₅ each represent at least one selected from the group consistingof —CH₂OH, —H, and —CH₂OR₁₈, and alkyl, alkenyl, alkynyl, alkoxyl,alkylthio, hydroxyalkyl and acyl having carbon numbers in the range of 1to 12, at least one of the R₁₂, R₁₃, R₁₄, and R₁₅ is —CH₂OH or —H, andat least two of the R₁₂, R₁₃, R₁₄, and R₁₅ are —CH₂OH, —H, or —CH₂OR₁₈;and R₁₆ and R₁₈each represent at least one selected from the groupconsisting of alkoxymethyl and acyloxymethyl having carbon numbers inthe range of 1 to 6, the R₁₆'s may be the same or different and theR₁₈'s may be the same or different.
 10. The field-effect transistoraccording to claim 7, wherein the hydroxyl group of the organic resin isa phenolic hydroxyl group.
 11. The field-effect transistor according toclaim 10, the organic resin having the phenolic hydroxyl group is apolyvinylphenol resin and/or a phenol resin.
 12. The field-effecttransistor according to claim 7, wherein the insulating layer has avolume resistivity of about 1×10¹³ Ω·cm or more.
 13. The field-effecttransistor according to claim 7, wherein the organic semiconductor layercontains a porphyrin compound.
 14. The field-effect transistor accordingto claim 7, further comprising a substrate containing a resin.